1. Field of the Invention
The invention relates to a wear part of a diamond-containing composite material and to a method for the production of such a wear part.
The term “wear part,” also referred to as a wearing part, is understood to mean a component that is subjected to a high degree of wearing stress. Depending on the stress, a broad diversity of materials are used, such as hardened steels, high-speed tool steels, stellites, hard metals and hard materials. In view of the growing requirements for wear resistance, there is increasing interest in diamond-containing composite materials or material composites.
U.S. Pat. No. 4,124,401 describes a poly-crystalline diamond material, wherein the individual diamond grains are held together by silicon carbide and a metal carbide or metal silicide. Materials according to the patent, although very hard, can be machined into shape only in a highly complicated way.
European patent publication EP 0 116403 discloses a diamond-containing composite material which consists of 80 to 90% by volume of diamond and 10 to 20% by volume of an Ni- and Si-containing phase. The Ni component is present as Ni or Ni silicide, and the Si component is present as Si, SiC or Ni silicide. No further phase constituents are present between the diamond grains. In order to achieve a sufficient bond between the individual diamond grains, sintering temperatures>1400° C. are required. Since diamond is no longer stable at these temperatures under normal pressure conditions, according to the pressure/temperature graph correspondingly high pressures are required in order to avoid a decomposition of the diamond. The plants necessary for this purpose are costly. Moreover, the diamond composite material produced in this way has very low fracture toughness and poor machinability.
A method for producing a diamond/silicon-carbide composite material is described in international PCT publication WO 99/12866. Production takes place by the infiltration of a diamond skeleton with silicon or with a silicon alloy. On account of the high melting point of silicon and the high infiltration temperature due to this, diamond is converted to a high degree into graphite or, further on, into silicon carbide. Owing to the high brittleness, the mechanical machinability of this material presents very serious problems and is complicated.
U.S. Pat. No. 4,902,652 describes a method for producing a sintered diamond material. There, an element from the group of transition metals of the groups 4a, 5a and 6a of the periodic table, boron and silicon is deposited onto diamond powder by way of physical coating methods. Subsequently, the coated diamond grains are bonded to one another by way of a solid-phase sintering process. The resulting product thus obtained, disadvantageously, has high porosity, low fracture toughness, and poor machinability.
U.S. Pat. No. 5,045,972 describes a composite material, wherein, in addition to diamond grains with a size of 1 to 50 μm, there is a metal matrix which consists of aluminium, magnesium, copper, silver or their alloys. The disadvantage there is that the metal matrix is bound only deficiently to the diamond grains, so that the mechanical integrity is not afforded to a sufficient extent as a result. Also, the use of finer diamond powder, for example with a grain size<3 μm, as may be gathered from U.S. Pat. No. 5,008,737, does not improve the diamond/metal bond.
U.S. Pat. No. 5,783,316 describes a method wherein diamond grains are coated with W, Zr, Re, Cr or Ti, the coated grains are then compacted, and the porous body is infiltrated. The infiltration is effected, for example, with Cu, Ag or Cu/Ag melts. The high coating costs and insufficient wear resistance limit the field of use of composite materials produced in this way.